Antihalation compositions

ABSTRACT

Antihalation compositions and methods for reducing the reflection of exposure radiation of a photoresist overcoated said compositions. The antihalation compositions of the invention comprise a resin binder and material capable of causing a thermally induced crosslinking reaction of the resin binder.

This is a continuation of application Ser. No. 07/792,482 filed on Nov.15, 1991 now U.S. Pat. No. 6,165,697.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to compositions that reduce the reflectionof exposure radiation from a substrate back to an overcoated resistlayer. More particularly, the invention relates to an antihalationcomposition characterized in one aspect by containing a thermallyactivated crosslinking agent.

2. Background Art

Photoresists are used for transfer of an image to a substrate. A coatinglayer of a photoresist is formed on a substrate, and the resist layer isthen selectively exposed through a photomask to a source of activatingradiation. The photomask has areas that are opaque to activatingradiation and other areas that are transparent to activating radiation.Exposure to activating radiation provides a photoinduced chemicaltransformation of the photoresist coating to thereby transfer thepattern of the photomask to the resist coated substrate. Followingexposure, the photoresist is developed to provide a relief image thatpermits selective processing of the substrate.

A photoresist can be either positive-acting or negative-acting. For mostnegative photoresists, those coating layer portions that are exposed toactivating radiation polymerize or crosslink in a reaction between aphotoactive compound and polymerizable reagents of the resistcomposition. Consequently, the exposed coating portions are renderedless soluble in a developer solution than unexposed portions. For apositive-acting photoresist, exposed portions are rendered more solublein a developer solution while areas not exposed remain comparativelyless developer soluble. The background of photoresists are described byDeforest, Photoresist Materials and Processes, McGraw Hill Book Company,New York, ch. 2, 1975, and by Moreay, Semiconductor Lithography,Principles, Practices and Materials, Plenum Press, New York, ch. 2 and4, both incorporated herein by reference for their teaching ofphotoresists and methods of making and using same.

A major use of photoresists is in semiconductor manufacture where anobject is to convert a highly polished semiconductor slice, such assilicon or gallium arsenide, into a complex matrix of electronconducting paths, preferably of micron or submicron geometry, thatperform circuit functions. Proper photoresist processing is a key toattaining this object. While there is a strong interdependency among thevarious photoresist processing steps, exposure is believed to be one ofthe most important steps in attaining high resolution photoresistimages.

Reflection of the activating radiation used to expose a photoresistoften poses notable limits on resolution of the image patterned in theresist layer. Reflection of radiation from the substrate/resistinterface can produce variations in the radiation intensity in theresist during exposure, resulting in non-uniform photoresist linewidthupon development. Radiation also can scatter from the substrate/resistinterface into regions of the resist where exposure is not intended,again resulting in linewidth variations. The amount of scattering andreflection will typically vary from region to region, resulting infurther linewidth non-uniformity.

Reflection of activating radiation also contributes to what is known inthe art as the “standing wave effect”. To eliminate the effects ofchromatic aberration in exposure equipment lenses, monochromatic orquasimonochromatic radiation is commonly used in resist projectiontechniques. Due to radiation reflection at the resist/substrateinterface, however, constructive and destructive interference isparticularly significant when monochromatic or quasi-monochromaticradiation is used for photoresist exposure. In such cases the reflectedlight interferes with the incident light to form standing waves withinthe resist. In the case of highly reflective substrate regions, theproblem is exacerbated since large amplitude standing waves create thinlayers of underexposed resist at the wave minima. The underexposedlayers can prevent complete resist development causing edge acuityproblems in the resist profile. The time required to expose thephotoresist is generally an increasing function of resist thicknessbecause of the increased total amount of radiation required to expose anincreased amount of resist. However, because of the standing waveeffect, the time of exposure also includes a harmonic component whichvaries between successive maximum and minimum values with the resistthickness. If the resist thickness is non-uniform, the problem becomesmore severe, resulting in variable linewidth control.

Variations in substrate topography also give rise to resolution-limitingreflection problems. Any image on a substrate can cause impingingradiation to scatter or reflect in various uncontrolled directions,affecting the uniformity of resist development. As substrate topographybecomes more complex with efforts to design more complex circuits, theeffects of reflected radiation become more critical. For example, metalinterconnects used on many microelectronic substrates are particularlyproblematic due to their topography and regions of high reflectivity.

Such radiation reflection problems have been addressed by the additionof certain dyes to photoresist compositions, the dyes absorbingradiation at or near the wavelength used to expose the photoresist.Exemplary dyes that have been so employed include the coumarin family,methyl orange and methanil yellow. Some workers have found that use ofsuch dyes can limit resolution of the patterned resist image.

Another approach has been to use a radiation absorbing layer interposedbetween the substrate surface and the photoresist coating layer. See,for example, PCT Application WO 90/03598, and U.S. Pat. Nos. 4,910,122,4,370,405 and 4,362,809, all of which are incorporated herein byreference for their teaching of antireflective (antihalation)compositions and use of the same. At least some prior antireflectivecoatings, however, suffer from poor adhesion to the overcoatedphotoresist layer and/or the underlying substrate surface. Such adhesionproblems can severely compromise the resolution of the patternedphotoresist image.

Thus, it would be desirable to have an antihalation coating compositionthat absorbs significantly incident and reflective exposure radiation,and that provides substantial standing wave attenuation. It would befurther desirable to have an antihalation composition that can be coatedon a microelectronic substrate and adhere well to both a subsequentlyapplied photoresist coating layer and the underlying substrate surface.

SUMMARY OF THE INVENTION

The present invention provides an antihalation composition suitable foruse with a photoresist, the antihalation composition in generalcomprising a resin binder and a compound capable of causing a thermallyinduced crosslinking reaction of the resin binder. Components of theantihalation composition preferably can crosslink with an overcoatedlayer of the photoresist composition, thereby increasing adhesionbetween the two coating layers and avoiding notable problems of at leastsome prior antireflective systems. The antihalation compositions of theinvention may further comprise an acid or acid generator compound tocatalyze the reaction between the resin binder and the crosslinkingcompound, enabling the crosslinking reaction to proceed at relativelylower temperatures. As used herein, the term acid generator refers to acompound that generates an acid upon appropriate treatment of thecompound, for example, upon exposure to activating radiation or thermaltreatment. The thermally active crosslinker can be a variety ofmaterials and, preferably, is an amine-based material such as abenzoguanamine-based or melamine-based resin. To enhance radiationabsorption properties, the antihalation compositions of the inventionmay further include one or more dye compounds that absorb radiation ator near the exposure wavelength of the overcoated photoresist.

The invention further provides a method for application and use of theantihalation coating composition with a photoresist. Thus, in apreferred aspect, a method is provided comprising (a) applying a layerof an antihalation composition of the invention on a substrate; (b) atleast partially curing the antihalation coating layer; (c) applying alayer of a photoresist on the coated substrate; (d) exposing selectedportions of the photoresist layer; (e) baking the applied antihalationand photoresist coating layers; and (f) developing the exposedphotoresist layer. When a suitable photoresist is employed, baking ofthe two coating layers results in crosslinking between components of theantihalation and photoresist compositions, thereby providing excellentadhesion between the two coating layers. It has also been found that theantihalation compositions of the invention adhere well to substratesurfaces, including substrates used in microelectronic applications.

The invention further provides methods for forming a relief image andnovel articles of manufacture consisting of substrates coated with anantihalation composition of the invention alone or in combination with aphotoresist composition. In particular, a coated substrate is provided,the substrate having an antihalation composition of the invention coatedthereon, and a photoresist coated over said antihalation composition,the photoresist comprising a resin binder and a radiation sensitivecomponent.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE illustrates schematically processes of the invention.

DETAILED DESCRIPTION OF THE INVENTION

A preferred antihalation composition of the invention comprises amixture of materials that will crosslink, cure or harden upon thermaltreatment. More particularly, a preferred composition comprises a resinbinder and a material capable of undergoing a thermally inducedcrosslinking reaction with said resin binder. Preferably the resinbinder and the thermal crosslinking compound are materials which, in anuncured state, are soluble in a nonreactive solvent or solvent mixtureand are capable of forming a homogeneous, nontacky, adherent film on asubstrate surface onto which it is applied.

A particularly preferred antihalation composition comprises anamine-based thermal crosslinker and a phenol-based resin binder.Suitable amine-based thermal crosslinkers include melamine-formaldehyderesins, glycoluril-formaldehyde resins, and urea-based resins. Suitablemelamine resins include the melamine resins manufactured by AmericanCyanamid Company of Wayne, N.J. and sold under the trade names Cymel®300, 301, 303, 350, 370, 380, 1116 and 1130. Suitable glycoluril resinsinclude those sold by the American Cyanamid Company under the tradenames of Cymel® 1170, 1171, 1172. Suitable urea-based resins includethose sold by the American Cyanamid Company under the trade names ofBeetle® 60, 65 and 80. A particularly preferred amine-based crosslinkeris a benzoguanamine-based material, including the benzoguanamine resinssold by the American Cyanamid Company under the trade names of Cymel®1123 and 1125. Additionally, combinations of the above amine-basedcrosslinkers will be suitable, including combinations that comprise abenzoquanamine-based material. In addition to the above resins availablefrom the American Cyanamid Company, a large number of similar resins arecommercially available from other suppliers. Additionally, suchamine-based resins may be prepared by the reaction of acrylamide ormethacrylamide copolymers with formaldehyde in an alcohol-containingsolution, or alternatively by the copolymerization of N-alkoxymethylacrylamide or methacrylamide with other suitable monomers. Thecrosslinker component of the antihalation compositions of the inventionin general are used in an amount of between about 5 and 50 weightpercent of total solids of the composition, more typically in amount of30 weight percent of total solids of the composition.

As noted above, the amine-based crosslinker compound of the antihalationcomposition is preferably used in combination with a phenol-based resinbinder. Suitable phenol-based resin binders include, for example,novolak resins; poly(vinylphenols) and copolymers of the same withstyrene, alpha-methylstyrene; acrylic resins; polyglutarimides;polyacrylic acid or polymethacrylic acid copolymers; alkali-solublepolyacrylamides and polymethacrylamide copolymers; copolymers containing2-hydroxyethylmethacrylate and 2-hydroxypropylmethacrylate; polyvinylalcohols such as those prepared from partially hydroxylated polyvinylacetates; alkali-soluble styrene-allyl alcohol copolymers; and mixturesthereof.

Of the above, poly(vinylphenol) and its copolymers and novolak resinscontaining hydroxyl groups and sites for the electrophilic substitutionof aromatic rings at positions ortho- or para- relative to the hydroxylgroup are preferred. Novolak resins that are useful in conjunction withamine-based resins in the acid hardening resin system are alkali-solublefilm forming phenolic resins having a molecular weight (weight average)ranging from about 300 to about 100,000 daltons, and preferably fromabout 1000 to 20,000 daltons. These novolak resins may be prepared bythe condensation reaction of a phenol, a naphthol or a substitutedphenol, such as, cresol, xylenol, ethylphenol, butylphenol, oxypropylmethoxyphenol, chlorophenol, bromophenol, resorcinol, naphthol,chloronaphthol, bromonaphthol or hydroquinone with formaldehyde,acetaldehyde, benzaldehyde, furfural acrolein, or the like. Blends ofsuitable novolak resins may also be used in order to adjust thedissolution rate of the exposed coating in aqueous base solutions aswell as for adjusting the viscosity, hardness and other physicalproperties of the coating. Suitable novolak resins are disclosed innumerous patents including U.S. Pat. Nos. 3,148,983; 4,404,357;4,115,128; 4,377,631; 4,423,138; and 4,424,315, the disclosures of whichare incorporated by reference herein.

Poly(vinylphenols) are thermoplastic materials that may be formed byblock polymerization, emulsion polymerization or solution polymerizationof corresponding monomers in the presence of a cationic catalyst.Vinylphenols used for the production of poly(vinylphenol) resins may beprepared, for example, by hydrolysis of commercially available coumarinsor substituted coumarins, followed by decarboxylation of the resultinghydroxy cinnamic acids. Useful vinyl phenols also may be prepared bydehydration of the corresponding hydroxy alkyl phenol or bydecarboxylation of hydroxy cinnamic acids resulting from the reaction ofsubstituted or non-substituted hydroxy benzaldehydes with malonic acid.Preferred poly(vinylphenol) resins prepared from such vinyl phenols havea molecular weight range of from about 2,000 to about 100,000 daltons.Procedures for the formation of polylvinylphenol) resins can be found inU.S. Pat. No. 4,439,516, incorporated herein by reference.

Another suitable phenol-based resin binder for use in the antihalationcompositions of the invention are copolymers of phenolic units andcyclic alcohol units analogous in structure to novolak resins andpoly(vinylphenol) resins. Such copolymers are described in U.S. patentapplication Ser. No. 07/354,800, incorporated herein by reference. Thesecopolymers may be formed in several ways. For example, in theconventional preparation of a poly(vinylphenol) resin, a cyclic alcoholmay be added to the reaction mixture as a comonomer during thepolymerization reaction which is thereafter carried out in a normalmanner. The cyclic alcohol is preferably aliphatic, but may contain oneor two double bonds. The cyclic alcohol is preferably one closest instructure to the phenolic unit. For example, if the resin is apoly(vinylphenol), the comonomer would be vinyl cyclohexanol.

The preferred method for formation of the copolymer compriseshydrogenation of a preformed poly(vinylphenol) resin. Hydrogenation maybe carried out using art recognized hydrogenation procedures, forexample, by passing a solution of the phenolic resin over a reducingcatalyst such as a platinum or palladium coated carbon substrate orpreferably over Raney nickel at elevated temperature and pressure. Thespecific conditions are dependent upon the polymer to be hydrogenated.More particularly, the polymer is dissolved in a suitable solvent suchas ethyl alcohol or acetic acid, and then the solution is contacted witha finely divided Raney nickel catalyst at a temperature of from about100 to 300° C. at a pressure of from about 50 to 300 atmospheres ormore. The finely divided nickel catalyst may be a nickel-on-silica,nickel-on-alumina, or nickel-on-carbon catalyst depending on the resinto be hydrogenated.

Another suitable resin binder for the antihalation compositions of theinvention is a polymer comprising anthracene units. This polymer maycontain other units such as carboxy and/or alkyl ester units pendantfrom the polymer backbone. In particular, a preferred resin binder has astructure of formula (I):

wherein R is a hydrogen or an alkyl group (e.g., an alkyl group havingfrom 1 to 6 carbon atoms); and x is the mole fraction of anthraceneester units in the polymer, and wherein x is suitably a value of from0.1 to 1.0. The anthracene groups may be unsubstituted or substituted atone or more available positions by substituents such as, for example,halo, alkoxy and alkyl. Suitably the anthracene moiety can besubstituted to a carboxyl group at any available position of theanthracene ring, as shown above in formula (I). Preferably, the resinbinder contains 9-anthracene ester units. These anthracene resin binderscan be prepared, for example, by condensation of anthranol withmethacryloyl chloride, followed by condensation of the vinyl anthraceneester reaction product to form the homopolymer, or condensation of thevinyl ester reaction product with other polymerizable compounds to forma mixed polymer.

For enhanced etch resistance of the antihalation composition, asilicon-containing material can be employed, such aspoly(vinylsilsesquioxane). Such a silicon-containing resin can be usedas the sole resin binder of the composition, or in combination withother resin binders, such as the phenolic resins described above.

The concentration of the resin binder component of the antihalationcompositions of the invention may vary within relatively broad ranges,and in general the resin binder is employed in a concentration of fromabout 50 to 95 weight percent of the total of the dry components of thecomposition, more typically from about 60 to 80 weight percent of thetotal dry components.

As indicated above, the antihalation compositions of the invention mayfurther comprise an acid or acid generator compound for catalyzing thecrosslinking reaction between the resin binder and crosslinker compound.Preferably an acid generator compound is employed. Suitable acidgenerator compounds include compounds that liberate acid upon photolysisor thermal treatment. Preferably a thermal acid generator is employed,i.e., a compound that generates acid upon thermal treatment. A varietyof known thermal acid generator compounds are suitably employed in theantireflective compositions of the invention such as, for example,2,4,4,6-tetrabromocyclohexadienone, benzoin tosylate, 2-nitrobenzyltosylate, and alkyl esters of organic sulfonic acids. Typically athermal acid generator is present in an antihalation composition inconcentration of from about 1 to 15 percent by weight of the total ofthe dry components of the composition, more preferably about 5 percentby weight of the total dry components. Photoacid generators may also beemployed in an antihalation composition, for example onium salts,halogenated non-ionic photoacid generators such as1,1-bis[p-chlorophenyl]-2,2,2-trichloroethane, and other photoacidgenerators disclosed herein for use in photoresist compositions.Suitable amounts of a photoacid generator in an antihalation compositionin general range from about 1 to 15 percent by weight of the total ofdry components of the composition. For an antihalation compositioncontaining a photoacid generator, a coating layer of the composition isexposed to an effective amount of activating radiation to generate thephotoacid, followed by a post-exposure bake at a temperature sufficientto at least partially cure the coating layer.

It should be appreciated that an antihalation composition of theinvention can be non-photoimageable, e.g., by not employing an acidcatalyst or employing a non-photoactive acid catalyst such as a thermalacid generator; or an antihalation composition can be renderedphotoimageable (and hence developable) by incorporating an effectiveamount of a suitable photoacid generator into the composition and thenexposing a coating layer of the composition through a photomask.Suitable photoacid generators include the non-ionic halogenetedphotoacid generators as described herein.

Another optional additive of the compositions of the invention arecompounds that serve as dyes and absorb radiation used to expose anovercoated photoresist layer. The dye should absorb well at thewavelength at which the overcoated photoresist is exposed and,therefore, selection of a suitable dye for a specific antihalationcomposition in large part will be determined by the particularphotoresist that is employed. For example, if an antireflectivecomposition is used in combination with a deep U.V. photoresist (i.e., aresist that is exposed at between 100 and 300 nm), the dye compoundshould strongly absorb in the deep U.V. region. Suitable dyes are knownin the art and include, for example, the curcumin family and derivativesthereof, anthracene, anthrarobin, Sudan-orange, benzophenothiazine andnaphthol-AS. Typically a dye is present in an antihalation compositionin a concentration of from about 2 to 30 percent by weight of the totalof the dry, components of the composition, more preferably from 5 to 15percent by weight of the total dry components.

Other optional additives include surface leveling agents, for example,the leveling agent available under the tradename Silwet 7604 from UnionCarbide.

To make a liquid coating composition, the components of the antihalationcomposition are dissolved in a suitable solvent such as, for example,one or more of the glycol ethers such as 2-methoxyethyl ether (diglyme),ethylene glycol monomethyl ether, and propylene glycol monomethyl ether;N-methyl pyrrolidinone; esters such as methyl cellosolve acetate, ethylcellosolve acetate, propylene glycol monomethyl ether acetate,dipropylene glycol monomethyl ether acetate and other solvents such asdibasic esters, propylene carbonate and gamma-butyro lactone. Theconcentration of the dry components in the solvent will depend onseveral factors such as the method of application. In general, thesolids content of an antihalation composition varies from about 1 to 50weight percent of the total weight of the antihalation composition,preferably the solids content varies from about 5 to 35 weight percentof the total weight of the antihalation composition.

A variety of photoresist compositions can be employed with theantihalation compositions of the invention. Preferably, a photoresist isemployed that, when coated over a film layer of antihalationcomposition, is capable of crosslinking with the antihalationcomposition at the interface of the two coating layers. Morespecifically, preferred photoresists for use with the antihalationcompositions of the invention include positive-acting andnegative-acting photoacid-generating compositions that comprise a resinsystem that can crosslink with one or more components of theantihalation composition.

A particularly preferred group of photoresists for use with thecompositions of the invention comprise a radiation sensitive componentsuch as a photoacid generator compound and a mixture of materials thatwill cure, crosslink or harden upon heating and exposure to acid. Apreferred mixture comprises a phenol-based resin binder and anamine-based crosslinker. Suitable phenol-based resins include novolakresins, poly(vinylphenols) and various copolymers thereof. Suitableamine-based crosslinkers include those described above for theantihalation compositions, in particular the melamine-formaldehyde Cymelresins available from American Cyanamid. Suitable photoacid generatorcompounds include the onium salts, such as those disclosed in U.S. Pat.Nos. 4,442,197, 4,603,101, and 4,624,912, each incorporated herein byreference; and non-ionic organic photoactive compounds such as thehalogenated photoactive compounds disclosed in the below referencedEuropean Patent Applications. These photoactive compounds should bepresent in a photoresist in an amount sufficient to enable developmentof a coating layer of the resist following exposure to activatingradiation. Preferred negative-acting photoresists for use in accordancewith the invention include the acid-hardening photoresists as disclosed,for example, in European Patent Applications Nos. 0401499 and 0423446,both incorporated herein by reference. As used herein, the term“acid-hardening photoresist” refers to photoresist compositions of thegeneral type described above and in these referenced European PatentApplications.

Other preferred photoresists include positive-acting photoresists thatcontain components that can crosslink with one or more components of theantihalation compositions of the invention. Such photoresists suitablycomprise a phenol-based resin binder in combination with a radiationsensitive component. Suitable resin binders include novolak resins,poly(vinylphenols) and various copolymers thereof. Suitable radiationsensitive components can comprise a variety of photoacid generatorcompounds including the naphthoquinone diazide sulfonic acid esters suchas 2,1,4-diazonaphthoquinone sulfonic esters and2,1,5-diazonaphthoquinone sulfonic acid esters; the onium salts; andother known acid generators such as those disclosed in European PatentApplication Nos. 0164248 and 0232972, both incorporated herein byreference. In addition to “conventional” positive-acting resists,chemically amplified positive resists are particularly suitable for usewith the antihalation compositions of the invention. As with the abovedescribed acid-hardening resists, a chemically amplified positive resistgenerates a catalytic photoproduct upon exposure to activatingradiation. In a positive system, this photoproduct (e.g., acid) rendersthe exposed regions of the resist more developer soluble, for example bycatalyzing a deprotection reaction of one or more of the resistcomponents to liberate polar functional groups such as carboxy. See,Lamola, et al., “Chemically Amplified Resists”, Solid State Technology,53-60 (August 1991), incorporated herein by reference.

Reference is now made to the FIGURE of the Drawing which shows apreferred method for use of an antihalation composition of theinvention. In Step A, an antihalation composition is applied tosubstrate 10 to provide antihalation coating layer 12. The antihalationcomposition may be applied by virtually any standard means includingspin coating. The antireflective composition in general is applied on asubstrate with a dried layer thickness of between about 0.05 and 0.5 μm,preferably a dried layer thickness of between about 0.10 and 0.20 μm.The substrate is suitably any substrate conventionally used in processesinvolving photoresists. For example, the substrate can be silicon,silicon dioxide or aluminum—aluminum oxide microelectronic wafers.Gallium arsenide, ceramic, quartz or copper substrates may also beemployed. Substrates used for liquid crystal display applications arealso suitably employed, for example glass substrates, indium tin coatedsubstrates and the like.

In Step B the antihalation layer is at least partially cured. Cureconditions will vary with the components of the antireflectivecomposition. Thus, if the composition does not contain an acid catalyst,cure temperatures and conditions will be more vigorous than those of acomposition containing an acid or acid generator compound. For example,for a composition containing a novolak resin binder and thebenzoquanamine-formaldehyde resin Cymel 1123 as a crosslinker, typicalcure conditions are heating at about 200° C. for about 30 minutes. Ifthe thermal acid generator 2,4,4,6-tetrabromocyclohexadienone is addedto this composition, cure temperatures of about 150° C. for about 30minutes will be suitable for at least partially curing the compositioncoating layer. Cure conditions preferably render coating layer 12substantially developer insoluble. Additionally, as discussed above, ifthe antihalation composition includes a photoacid generator, thecompoitloii coating layer can be at least partially cured by exposingthe coating layer to an effective amount of activating radiation (e.g.,between about 10 to 300 mJ/cm²), followed by a post-exposure bake offrom 50 to 140° C.

In Step C a photoresist is applied over the surface of the crosslinkedantihalation layer 12. As with application of the antihalationcomposition, the photoresist can be applied by any standard means suchas by spinning, dipping or roller coating. When spin coating, the solidscontent of the photoresist composition can be adjusted to provide adesired film thickness based upon the specific spinning equipmentutilized, the viscosity of the solution, the speed of the spinner andthe amount of time allowed for spinning. Following application, thephotoresist coating layer 14 is typically dried by heating to removesolvent preferably until layer 14 is tack free. Optimally, nointermixing of the antihalation layer and photoresist layer shouldoccur.

In Step D coating layer 14 is imaged with activating radiation through amask in conventional manner. The exposure energy is sufficient toeffectively activate the photoactive component of the radiationsensitive system to produce a patterned image 16 in coating layer 14and, more specifically, the exposure energy typically ranges from about10 to 300 mJ/cm², dependent upon the exposure tool.

Step E is an optional step and is employed if the photoresist requirespost-exposure heating to create solubility differences between exposedand unexposed regions of a coating layer. For example, acid-hardeningphotoresists typically require post-exposure heating to induce theacid-catalyzed crosslinking reaction, as depicted in Step E′; and manychemically amplified positive-acting resists require post-exposureheating to induce an acid-catalyzed deprotection reaction as shown inStep E″. Typically the coated substrate 10 is subjected to apost-exposure bake at temperatures of from about 50° C. or greater, morespecifically a temperature in the range of from about 50° C. to 140° C.

In Step F, the exposed resist coating layer 14 is developed, preferablywith an aqueous based developer such as an inorganic alkali exemplifiedby sodium hydroxide, potassium hydroxide, sodium carbonate, sodiumbicarbonate, sodium silicate, sodium metasilicate, aqueous ammonia orthe like. Alternatively, organic developers can be used such as cholinebased solutions; quaternary ammonium hydroxide solutions such as atetra-alkyl ammonium hydroxide solution; various amine solutions such asethyl amine, n-propyl amine, diethyl amine, di-n-propyl amine, triethylamine or, methyldiethyl amine; alcohol amines such as diethanol amine ortriethanol amine; cyclic amines such as pyrrole, piperidine, etc. Ingeneral, development is in accordance with art recognized procedures.

Following development, a final bake of an acid-hardening photoresist isoften employed at temperatures of from about 100 to 150° C. for severalminutes to further cure the developed exposed areas 16.

The developed substrate may then be selectively processed on thosesubstrates areas bared of photoresist, for example chemically etching orplating substrate areas bared of photoresist in accordance withprocedures well known in the art. Suitable etchants include ahydrofluoric acid etching solution and a plasma gas etch such as anoxygen plasma etch. In particular, a plasma gas etch readily penetratesthe crosslinked antihalation coating layer.

It should be appreciated that the same removal chemistry can be employedto strip both an antihalation composition of the invention and manyphotoresists used in combination therewith. For example, anacid-hardening photoresist used in combination with a preferredantihalation composition of the invention comprising a phenol-basedresin binder and an amine-based crosslinker as described above, isreadily stripped with a single stripper solution after selectivesubstrate treatment. For removing such coating layers, a preferredstripper solution contains about 90 weight percent dimethylsulfoxide and10 weight percent para-toluenesulfonic acid. Preferably this compositionis used at about 70 to 90° C.

The following examples are presented to better illustrate the invention,but are not to be construed as limiting the invention to the specificembodiments disclosed. In the antihalation compositions disclosed in theexamples, the novolak resin component was a formaldehyde-phenolcondensate, the phenol component being 95 weight percent cresol and 5weight percent ethylphenol, and the resin having a molecular weight(weight average) of about 11,000 daltons and a dispersity of about 20.

EXAMPLE 1

A preferred antihalation composition was prepared by mixing thecomponents set forth below, with component amounts expressed as parts byweight:

Component Amount Resin binder 5.59 Novolak resin Crosslinker material1.67 Hexamethoxymethylmelamine (obtained from American Cyanamid) Thermalacid generator 0.28 2,4,4,6-tetrabromocyclohexadienone Surface levelinqagent 0.015 Silwet 7604 (obtained from Union Carbide) Solvent diglyme33.96 anisole 11.31

This antihalation composition was examined to determine the curingtemperature necessary to render a film layer of the compositioninsoluble in aqueous developer. The solution was spin coated at 4000r.p.m. onto seven vapor-primed (HMDS vapor, room temperature andpressure, 3 minutes) 4 inch silicon wafers. These wafers were softbakedfor 60 seconds on a vacuum hotplate, each wafer baked at differenttemperatures, specifically each wafer was baked at 20° C. temperatureincrements in a range of from 80-200° C. Film thickness was determinedfrom seven measurements on a Nanometrics Nanospec 215 using a refractiveindex of 1.64. The seven wafers were batch-developed for 60 seconds inroom temperature Microposit® MF-321 developer (an aqueoustetramethylammonium hydroxide (TMAH) solution available from ShipleyCo., Newton, Massachusetts) at a normality of 0.21 and then againmeasured for film thickness again, as described above using a Nanospec215. It was found that a bake temperature of 120° C. or greater wassufficient to crosslink the antihalation coating layer so as to make itinsoluble in the 0.21 N TMAH developer.

EXAMPLE 2

The antihalation composition of Example 1 was tested for absorbance inthe deep U.V. region. The composition was spin-coated at 3000 r.p.m.onto a 3-inch quartz wafer and softbaked at 120° C. for 60 seconds on avacuum hotplate. Thickness was estimated by coating a 4 inch siliconwafer under the same conditions and measuring its thickness on aNanospec 215, as described in Example 1 above. The coated wafer wasanalyzed on a Hewlett-Packard HP8452A UV-Visible Spectrophotometer andthen corrected for the absorbance of the quartz wafer. At an exposurewavelength of 248 nm, the formulation was found to have an absorbance of1.371 absorbance units per micron of thickness.

EXAMPLE 3

The antihalation composition of Example 1 was coated at 3000 r.p.m. onto4 vapor-primed (HMDS, by procedures described in Example 1) 4 inchsilicon wafers; the wafers were softbaked for 60 seconds on a vacuumhotplate. Two wafers were baked at 140° C., and the other two waferswere baked at 160° C. The four wafers were then each overcoated withMegaposit SNR248-1.0 deep UV photoresist (an acid-hardening photoresistsold by the Shipley Co.), using a 30 second spin at 3660 r.p.m.,followed by a 60 second softbake at 90° C. on a vacuum hotplate in orderto generate a resist layer thickness of approximately 1.025 microns. Thewafers were exposed on a GCA Laserstep excimer laser stepper operatingat the wavelength of 248 nm; an 8×8 array of patterns was utilized,covering a wide range of both exposure and focus to ensure that theoptimum exposure was attained. The wafers were split up into two groups,each group containing one coated wafer cured at 140 C, and anothercoated wafer cured at 160° C.; one group of wafers was processed with a60 second vacuum hotplate post-exposure bake at 110° C. while the othergroup was baked at 140° C. All of the wafers were developed with 0.14 NTMAH MF-319 developer (Shipley Co.) in double puddle mode, using 25 and50 second puddles and a total developer contact time of 100 seconds.Well resolved lines/spaces (including lines having essentially verticalsidewalls) of down to 0.34 μm were patterned on the antihalation coatinglayer.

EXAMPLE 4

Another preferred antihalation composition was prepared by mixing thecomponents set forth below, with component amounts expressed as parts byweight:

Component Amount Resin binder 3.462 Novolak Crosslinker material 1.039Ethylated/methylated benzoguanamine- formaldehyde resin (sold under thetradename Cymel 1123 by American Cyanamid) Solvent 25.500Diethyleneglycoldimethylether

This antihalation composition was spin coated at 4600 r.p.m. ontovapor-primed (HMDS, room temperature and pressure, 3 minutes) 4 inchsilicon wafers and unprimed 4 inch quartz wafers; each wafer wassoftbaked at 125° C. for 60 seconds on a vacuum hotplate. The waferswere then baked for 30 minutes in a Blue M convection oven. Thicknessanalysis of the antihalation composition coated silicon wafers on aNanometrics Nanospec 215 showed an average film thickness of 1733angstroms. The quartz wafers were analyzed on a Cary3 UV-VisibleSpectrophotometer; after correcting for the absorbance of the quartzwafer, the absorbance of the 1733 angstroms thick antihalation coatedquartz wafer was found to be 0.719 (absorbance units) at the wavelengthof 248 nm. Next, one coated silicon wafer was overcoated with Megaposit®SNR248-1.0 photoresist, and another coated silicon wafer was overcoatedwith MicropositR XP-89131 photoresist, both said photoresists availablefrom the Shipley Co. The coating of the Megaposit SNR248 resist requireda 30 second spin at 3680 r.p.m. and a 60 second softbake at 90° C. on avacuum hotplate in order to generate a thickness of approximately 1.014microns, whereas the Microposit XP-89131 resist utilized a 3760 r.p.m.spin and a 110° C. softbake temperature to achieve a coating layerthickness 1.017 microns. The two wafers were exposed on a GCA Laserstepexcimer laser stepper operating at the wavelength of 248 nm; a 7-by-15array of patterns was utilized, covering a wide range of both exposureand focus to ensure that the optimum exposure was attained. All of thewafers were post-exposure baked at 130° C. for 60 seconds on a vacuumhotplate and then developed with XP-89114 developer aqueous (TMAHdeveloper available from the Shipley Co.) in double puddle mode, using25 and 50 second puddles and a total developer contact time of 100seconds. Well resolved lines/spaces (including lines having essentiallyvertical sidewalls) of down to 0.36 μm were patterned on theantihalation coating layer.

The foregoing description of the invention is merely illustrativethereof, and it is understood that variations and modifications can beeffected without departing from the scope or spirit of the invention asset forth in the following claims.

What is claimed is:
 1. An antihalation coating comprising a resin binderand a crosslinker compound capable of causing crosslinking reaction ofthe resin binder said resin binder conforming to the formula:

where x varies between 0.1 and 1.0, R is hydrogen or alkyl and R′ is amember selected from the group consisting of hydrogen, alkyl, halo andalkoxy.
 2. The composition of claim 1 where R′ is alkyl.
 3. The coatingof claim 1 further comprising a compound selected from the groupconsisting of an acid and an acid generator compound.
 4. The coating ofclaim 1 further comprising a thermal acid generator.
 5. The coating ofclaim 1 further comprising a radiation absorbent dye.
 6. The coating ofclaim 1 where the crosslinker is an amine-based material.
 7. The coatingof claim 1 where the crosslinker is a melamine resin.
 8. The coating ofclaim 1 where the cross-linker is a glycoluril-formaldehyde resin.